Print head ink flow path with bubble removal grooves

Abstract

A print head includes an inlet port that receives a flow of a phase-change ink and an outlet port that delivers the flow to a jet. The print head includes a flow path along a flow direction from the inlet port to the outlet port. The flow path has top and bottom planar surfaces, and further includes two or more elongated grooves in at least one of the top and bottom planar surfaces. The two or more elongated grooves are at an angle to the flow direction and have a threshold capillary dimension such that bubbles in the phase-change ink are directed along the elongated grooves.

What is claimed is: 
     
       1. A print head comprising:
 an inlet port that receives a flow of a phase-change ink; 
 an outlet port that delivers the flow to a jet; and 
 a flow path along a flow direction from the inlet port to the outlet port, the flow path comprising:
 top and bottom planar surfaces; and 
 two or more elongated grooves in at least one of the top and bottom planar surfaces, the two or more elongated grooves at an angle to the flow direction, the elongated grooves comprising a threshold capillary dimension such that bubbles in the phase-change ink are directed along the elongated grooves, wherein the threshold capillary dimension is satisfied if μUH/σ*w<1, wherein μ is a fluid viscosity of the phase-change ink, U is a characteristic fluid velocity in the flow path, H is a height of the flow path, σ is a surface tension of the bubbles, and w is a length scale of the bubbles. 
 
 
     
     
       2. The print head of  claim 1 , wherein the flow is driven by buoyancy. 
     
     
       3. The print head of  claim 1 , wherein the flow is driven by a pressure differential between the inlet port and the outlet port. 
     
     
       4. The print head of  claim 1 , wherein the elongated grooves are spaced apart such that any of the bubbles that are pushed past a first of the elongated grooves by the flow are captured by a second of the elongated grooves. 
     
     
       5. The print head of  claim 1 , further comprising:
 a second planar flow path separated from the flow path by a layer; and 
 a tapered via through the layer joining at least one elongated groove of the flow path and the second planar flow path, wherein the bubbles are directed through the tapered via to the second planar flow path. 
 
     
     
       6. The print head of  claim 5 , wherein the second planar flow path directs the bubbles to a vent. 
     
     
       7. The print head of  claim 5 , wherein the second planar flow path comprises a second elongated groove having the threshold capillary dimension, the tapered via joining the at least one elongated groove with the second elongated groove. 
     
     
       8. The print head of  claim 1 , further comprising an obstruction in the flow path between two of the elongated grooves, the obstruction causing the bubbles to be directed to one or the other of the two elongated grooves. 
     
     
       9. The print head of  claim 1 , further comprising a vent, wherein the elongated grooves are disposed to direct the bubbles to the vent. 
     
     
       10. The print head of  claim 9 , wherein the bubbles are directed to the vent responsive to a pulse of flow pressure followed by a period of no flow pressure, wherein buoyancy forces during the period of no flow pressure guide the bubbles along the elongated grooves towards the vent. 
     
     
       11. The print head of  claim 1 , wherein the elongated grooves induce a secondary flow in the flow path, the secondary flow causing smaller bubbles to be moved in a direction along the elongated grooves, the smaller bubbles being too small to be trapped by the elongated grooves. 
     
     
       12. A method, comprising:
 applying pressure to phase-change ink in a flow path, the flow path comprising top and bottom planar surfaces, and two or more elongated grooves in at least one of the top and bottom planar surfaces, the two or more elongated grooves at an angle to a flow direction and comprising a threshold capillary dimension such that bubbles in the phase-change ink are directed along the elongated grooves, the threshold capillary dimension being satisfied if μUH/σ*w<1, wherein μ is a fluid viscosity of the phase-change ink, U is a characteristic fluid velocity in the flow path, H is a height of the flow path, σ is a surface tension of the bubbles, and w is a length scale of the bubbles; and 
 removing the pressure to allow the bubbles to be moved via buoyancy, wherein the applying of the pressure and the removing of the pressure are repeated a plurality of times. 
 
     
     
       13. The method of  claim 12 , wherein the moving of the bubbles via buoyancy causes the bubbles to coalesce into larger bubbles. 
     
     
       14. The method of  claim 12 , further comprising obstructing the flow path between two of the elongated grooves to cause the bubbles to be directed to one or the other of the two elongated grooves. 
     
     
       15. A print head comprising:
 first and second planar flow paths separated by a layer, the first planar flow path comprising two or more elongated grooves in a planar surface, the two or more elongated grooves at an angle to a flow direction of a phase-change ink, the elongated grooves comprising a threshold capillary dimension that results in a surface tension force acting on bubbles being greater than a force of the flow acting on the bubbles such that the bubbles are directed along the elongated grooves, wherein the threshold capillary dimension is satisfied if μUH/σ*w<1, wherein μ is a fluid viscosity of the phase-change ink, U is a characteristic fluid velocity in the flow path, H is a height of the flow path, σ is a surface tension of the bubbles, and w is a length scale of the bubbles; and 
 a via through the layer joining at least one elongated groove of the first planar flow path to the second planar flow path, wherein the bubbles are directed through the via to the second planar flow path by the flow. 
 
     
     
       16. The print head of  claim 15 , wherein the second planar flow path comprises a second elongated groove having the threshold capillary dimension, the via joining the at least one elongated groove with the second elongated groove. 
     
     
       17. The print head of  claim 16 , wherein the via is tapered. 
     
     
       18. The print head of  claim 15 , wherein the second planar flow path directs the bubbles to a vent.